A battery powered user-wearable device includes a light source and a light detector and is configured to obtain at least two different types of physiological measurements using the light source and the light detector. During a first period of time, the user-wearable device is operated in accordance with a first operational mode that is used to obtain a first type of physiological measurement. In the first operational mode the light source is driven to emit pulses of light at a low frequency. During a second period of time, the user-wearable device is operated in accordance with a second operational mode that is used to obtain a second type of physiological measurement. In the second operational mode the light source is either driven to continually emit light or is driven to emit pulses of light at a high frequency. The first operational mode consumes less power than the second operational mode.
